The applicant has developed electron emitting devices having a novel structure, which are capable of operating in the atmospheric air (see, for example, Patent Documents 1 and 2).
The electron emitting device which is described in Patent Document 2 includes a semi-conductive layer which is interposed between a pair of electrodes (i.e., a substrate electrode and a surface electrode), the semi-conductive layer being composed of a dielectric material with electrically conductive nanoparticles dispersed therein. By applying a voltage on the order of several dozen volts to the semi-conductive layer, electrons can be emitted from the surface electrode (field electron emission). Therefore, unlike any conventional electron emitting device (e.g., a corona discharger) that utilizes a discharge phenomenon under a strong field, this electron emitting device has an advantage in that ozone will not be generated.
This electron emitting device can be suitably used as a charger device for charging a photosensitive drum of an image forming apparatus (e.g., a copier machine), for example. According to Non-Patent Document 1, an electron emitting device that includes a surface electrode of the layered structure described in Patent Document 2 may have a lifetime of about 300 hours (equivalent to approximately 300,000 sheets in the case of a medium-fast copier machine) or more.